﻿// 锚点(Anchor)间平滑跳转
$.scroller = function (el, duration, offsetY) {
    function intval(v) {
        v = parseInt(v);
        return isNaN(v) ? 0 : v;
    }

    // 获取元素信息
    function getPos(e) {
        var l = 0;
        var t = 0;
        var w = intval(e.style.width);
        var h = intval(e.style.height);
        var wb = e.offsetWidth;
        var hb = e.offsetHeight;
        while (e.offsetParent) {
            l += e.offsetLeft + (e.currentStyle ? intval(e.currentStyle.borderLeftWidth) : 0);
            t += e.offsetTop + (e.currentStyle ? intval(e.currentStyle.borderTopWidth) : 0);
            e = e.offsetParent;
        }
        l += e.offsetLeft + (e.currentStyle ? intval(e.currentStyle.borderLeftWidth) : 0);
        t += e.offsetTop + (e.currentStyle ? intval(e.currentStyle.borderTopWidth) : 0);
        return { x: 0, y: t, w: w, h: h, wb: wb, hb: hb };
    }

    // 获取滚动条信息
    function getScroll() {
        var t, l, w, h;

        if (document.documentElement && document.documentElement.scrollTop) {
            t = document.documentElement.scrollTop;
            l = document.documentElement.scrollLeft;
            w = document.documentElement.scrollWidth;
            h = document.documentElement.scrollHeight;
        } else if (document.body) {
            t = document.body.scrollTop;
            l = document.body.scrollLeft;
            w = document.body.scrollWidth;
            h = document.body.scrollHeight;
        }
        return { t: t, l: l, w: w, h: h };
    }


    if (typeof el != 'object') { el = document.getElementById(el); }

    if (!el) return;

    var z = this;
    z.el = el;
    z.p = getPos(el);
    z.p.y -= offsetY;
    z.s = getScroll();
    z.clear = function () { window.clearInterval(z.timer); z.timer = null };
    z.t = (new Date).getTime();

    z.step = function () {
        var t = (new Date).getTime();
        var p = (t - z.t) / duration;
        if (t >= duration + z.t) {
            z.clear();
            window.setTimeout(function () { z.scroll(z.p.y, z.p.x) }, 13);
        } else {
            st = ((-Math.cos(p * Math.PI) / 2) + 0.5) * (z.p.y - z.s.t) + z.s.t;
            sl = ((-Math.cos(p * Math.PI) / 2) + 0.5) * (z.p.x - z.s.l) + z.s.l;
            z.scroll(st, sl);
        }
    };
    z.scroll = function (t, l) { window.scrollTo(l, t) };
    z.timer = window.setInterval(function () { z.step(); }, 13);
}